Characterization of Fine Fractions from the Processing of Municipal Solid Waste Incinerator Bottom Ashes for the Potential Recovery of Valuable Metals

Sebastian Keber,Thomas Schirmer,Tobias Elwert,Daniel Goldmann

doi:10.3390/min10100838

Abstract

Municipal waste incinerator bottom ashes contain copper contents comparable to those of low-grade ores in addition to other valuable metals. While the processing of coarse fractions (>2 mm) is state of the art, the fines with their residual metal content are landfilled. This paper presents the results from a mineralogical characterization of fine fractions from the processing of municipal solid waste incinerator bottom ashes. From the results, possible approaches for a recovery of copper from the fine fraction are derived. Spatially resolved phase analysis reveals that the material contains a very heterogenic mixture of naturally occurring compounds as well as particles of alloys, metals, artificial oxides, and sulfides. The most interesting element to recover is copper. Copper can be found in the form of alloys, simple sulfides (XS), and oxides (XO). During the incineration process, new phases are generated that differ from natural ones and therefore can be called artificial minerals. Additionally, several components are partially altered due to oxidation, especially after the prolonged outside storage of the bottom ash. Crystalline silicate and glass particles are only sporadically enriched in Cu. Based on these results, different processing techniques are discussed. Due to the small particle size distribution and the physical and physico-chemical properties of the particles, flotation seems to be the most promising technique for the enrichment of copper from municipal solid waste incineration bottom ash (MSWI-BA) fine fractions.

Highlights

In the context of current efforts in the field of resource and energy efficiency, waste streams and deposits with fine-grained metals are getting increasing attention
The changes over time are smaller than expected, but it has to be considered that the samples originate from one processing plant which homogenizes large amounts of municipal solid waste incineration bottom ash (MSWI-BA) from a wide catchment area
In the case of outside storage over several weeks, the sulfide particles showed an oxide layer, which means that, during flotation, they would mostly behave like copper oxide particles

Summary

Introduction

In the context of current efforts in the field of resource and energy efficiency, waste streams and deposits with fine-grained metals are getting increasing attention. The reason for this is that reduction in environmental impact is driving recycling, as well as the potential to produce metal concentrates through recycling at lower costs than those of production from primary sources [1]. While the mineral phases of primary resources are well known and have been investigated for many decades, the mineral phases of waste streams have not been entirely identified yet Depending on their origin and occurring transformation processes, these phases include metals, alloys, and metal compounds that often have no natural equivalent. Examples of waste streams and residues which can contain those artificial phases are:

Methods

Results

Discussion

Conclusion